A reaction engineering approach to kinetic analysis of photocatalytic reactions in slurry systems

The knowledge of the rate equation is fundamental for the assessment of the activity of the photocatalyticmaterial and for the study, design and optimization of photocatalytic reactors. In the case of photocat-alytic reactions, the local volumetric rate of photon absorption (LVRPA) affects the reaction rate and itsinherently uneven distribution within a “slurry” reactor makes complex a correct kinetic analysis. In thepresent work it is shown which are the critical aspects of the kinetic analysis in slurry reactors and howto carry out photocatalytic experiments to minimize the misinterpretations of the experimental results.In particular, the influence of the type of illumination and of the operating conditions (recirculation flowrate, optical thickness) are studied. For instance, it is shown that the average values of the reaction rateand of the rate of photon absorption give no direct insight on the intrinsic kinetic if the reactor is notuniformly illuminated and the optical thickness is beyond a given value, which is significantly higherthan the one usually suggested in literature for a “safe” kinetic analysis. Furthermore, the estimation ofthe average rate of photon absorption must take into account the backscattering of radiation from thereactor. In any case, the utilization of a proper mathematical model allows carrying out a sound kineticanalysis also in critical situations as those which can arise with an illumination by LEDs.